Literally was modifying "just," not "finished." If he figuratively "just finished" one, he may have actually finished it yesterday or a few days ago, which would be a valid assumption if the "literally" modifier wasn't there. With the modifier, Zecronto was commenting on the coincidental nature of the fact that he wrote the post immediately after downing the rest of the bottle.

It's not that big of a deal, bro. You should literally cool down.